In an electrophotographic image forming apparatus such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine or a printer-copier-facsimile multifunction machine, a nonmagnetic single-component developing system is mainly employed as a developing system.
In the nonmagnetic single-component developing system, toner is passed through between a developing roller and a toner amount regulating blade to be triboelectrically charged and carried on an outer peripheral surface of the developing roller, whereby a toner layer is formed on the outer peripheral surface. Then, the toner layer thus formed is brought into direct contact with a surface of a photoreceptor body formed with an electrostatic latent image, whereby the toner is selectively transferred from the toner layer to the electrostatic latent image to develop the electrostatic latent image into a toner image. Alternatively, the toner layer is brought into noncontact adjacent relation to the surface of the photoreceptor body, whereby the toner is selectively transferred (or allowed to selectively jump) to the electrostatic latent image to develop the electrostatic latent image into a toner image.
The developing roller generally includes a roller body which includes a single layer formed, for example, by forming a semiconductive rubber composition into a tubular body and crosslinking rubber of the tubular body, or a plurality of layers including the aforementioned rubber layer.
In general, the outer peripheral surface of the roller body is conditioned into a proper surface state, for example, by polishing the outer peripheral surface, or coating the outer peripheral surface with a coating film after the polishing.
The coating film is formed by applying a liquid coating agent onto the outer peripheral surface of the roller body by a spray method, a dipping method or other coating method, and then drying the applied liquid coating agent. Therefore, the coating film is liable to suffer from contamination with foreign matter such as dust during the formation thereof, uneven thickness and other defects.
For preparation of the coating agent, an organic solvent is required. However, the use of the organic solvent may exert a great load on the environment, and go against a recent trend toward reduction of VOC (volatile organic compounds).
It is contemplated to form asperities of various shapes on the outer peripheral surface of the roller body, for example, by controlling conditions for the polishing or by performing a texturing process such as laser processing or blasting, rather than forming the coating film (see, for example, Patent Documents 1 to 6).